In the fields using electromagnetic motors such as robots, cutting machines, automobiles, etc., demand has been mounting to reduce the weight of driving systems. However, because the power densities of the electromagnetic motors depend on the weight of motors, the weight reduction of actuators utilizing the electromagnetic motors is limited. To obtain large power with reduced size and weight, actuators without using electromagnetic motors are desired.
As actuators which can be made smaller in size and weight, polymer actuators have recently been attracting much attention. Known as the polymer actuators are a gel actuator using a conductive polymer gel, a polymer membrane actuator using a conductive polymer membrane, etc.
In general, the conductive polymer membrane actuator comprises a conductive polymer membrane and metal electrodes formed thereon. The metal electrodes are formed on the surfaces of the conductive polymer membrane by such methods as chemical plating, electroplating, vapor deposition, sputtering, coating, pressure-bonding, welding, etc. When potential difference is provided to an assembly of a conductive polymer membrane and metal electrodes in a water-containing state, bending and deformation occur in the conductive polymer membrane, and they can be utilized as a driving force.
JP2003-152234A discloses an actuator comprising an electrolyte sandwiched by electrodes, whose shape changes when voltage is applied to the electrodes, each of the above electrodes being constituted by a conductive polymer, and a conductive material in electrical contact with the conductive polymer, the conductive material being in the form of powder, a net or a porous body. This actuator comprises a powdery conductive material layer, and a pair of conductive polymer membranes sandwiching the conductive material layer, the conductive material layer and the conductive polymer membrane being curved when electric current is supplied. It is described in JP2003-152234A that the conductive material in the form of powder, etc., can easily follow the shape change of the electrodes when voltage is applied, so that peeling does not occur when the conductive polymer layer is bent. However, because this actuator is displaced in a bent state, it is difficult to control the amount and position of displacement. In addition, though large power is generated when it contracts, only small power is generated when the polymer membrane extends. Accordingly, the displacement at the time of extension cannot be utilized, suggesting that this is not an efficient actuator.
JP2003-170400A discloses an actuator element comprising an anion-exchange resin molding, metal electrodes formed on the anion-exchange resin molding with insulation to each other, and conductive polymer membranes each formed on each metal electrode. In this actuator element, the conductive polymer membrane is formed on the metal electrode by an electrolytic polymerization method. When electric current is supplied between the metal electrodes, electric current flows through the anion-exchange resin molding sandwiched by the electrodes and through the conductive polymer membranes. The supply of electric current causes minus ions in the resin to migrate toward an anode, with water molecules also migrating together with the ions, so that the actuator element extends on the anode side. The conductive polymer membrane also extends by oxidation on the anode side and contracts by reduction on the cathode side. It is described in JP2003-170400A that the anion-exchange resin molding and the conductive polymer membranes synergistically generates large displacement.
In the actuator element described in JP2003-170400A, however, the electro-conductive polymer membrane is displaced by bending, resulting in difficulty in controlling the amount and position of displacement like in the actuator of JP2003-152234A, and the displacement at the time of extension cannot be utilized. In addition, the production of the conductive polymer membrane by electrolytic polymerization takes an extremely long period of time, thus costly.